This proposal describes the organization of a comprehensive, multidisciplinary international HIV Vaccine Trials Network (HVTN). Components of the HVTN include a Leadership Coordinating and Operations Center (L. Corey, Contact PI; S. Hammer and G. Gray, PI's); a Statistical and Data Management Center (P. Gilbert, PI) and a Network Laboratory Program (M. J. McElrath, PI). The HVTN's mission is to provide an objective and transparent platform to evaluate candidate HIV vaccines for the prevention of HIV infection in adult and adolescent populations globally. To achieve this, the HVTN will perform safety, immunogenicity, and efficacy trials of candidate HIV vaccines and adjuvants; conduct head-to-head comparisons of candidate vaccines; develop laboratory and statistical approaches to define potential correlates of protection; design trials to estimate the effects of vaccines tha reduce HIV acquisition and reduction in set point viremia transmission; conduct trials of candidate vaccines in special populations, such as adolescents and intravenous drug users; develop standardized risk reduction counseling methods; and collaborate with other NIH networks, federal agencies and non-governmental research organizations to advance the highest quality HIV vaccine research with optimal efficiency and cost effectiveness.